The invention is directed to a method for synchronously retracting and extending a jib of a crane having a plurality of telescoping lengths, preferably in a vehicle crane, wherein jib extending and retracting is with driving means which is one of hydaulically-driven, multistage telescoping cylinder or a plurality of single stage telescoping cylinders operated in parallel.
Various telescoping systems have long been established in crane construction in the field of telescopic jibs. In one instance, a single-stage piston-cylinder unit is used as driving means for retracting and extending the individual telescoping lengths and these telescoping lengths are secured after retraction or extension by means of adjustable locking pins (EP 0 661 234). In another instance, a telescoping system is used in which the telescoping lengths which are mechanically connected with one another via cables or chains can retract and extend synchronously (DE-OS 19 06 483, DE 31 25 603 A1). The synchronous retraction and extension of the telescoping lengths is also possible by means of a multistage piston-cylinder unit which is connected at the head side with the innermost length (EP 0 460 476 A1).
It is the object of the invention to provide a method for synchronous retraction and extension of a jib of a crane having a plurality of telescoping lengths by which a defined maximum suspended load can be assigned to the respective extension length continuously during the entire telescoping process and which prevents asynchronism.
In the proposed method, for synchronously retracting and extending a jib of a crane having a plurality of telescoping lengths, wherein jib retracting and extending is with driving means which is one of a hydraulically-driven multistage telescoping cylinder, and a plurality of single-stage telescoping cylinders operated in parallel, a pilot transmitter or precontrol transmitter transmits an electrical signal to an input of a regulating electronics arrangement. This signal serves as a reference value for the telescoping speed of a telescoping cylinder or stage which takes on the task of guiding. The actual value of a present position of the telescoping cylinders or stages is reported to the regulating electronics arrangement. The regulating electronics arrangement compares the actual value of the telescoping cylinder or stage assuming the guidance task to the actual value of the rest of the telescoping cylinders or stages to be controlled, i.e., the telescoping cylinders or stages. In the event that an impermissible deviation is determined, i.e., within the framework of tolerances inherent to the system, the telescoping speed of the rest of the telescoping cylinders or stages is increased or reduced until a synchronous telescoping of all telescoping cylinders and stages occurs.
The advantage of the proposed solution consists in that asynchronism of the telescoping process is prevented in a very simple manner.
The synchronous regulation of the telescoping jib is activated by a switch; in the present example, the jib has two retractable and two extensible telescoping lengths. The telescoping cylinders are retracted and extended by the pre-control transmitter.
When retracting, a check is carried out initially to determine whether or not a synchronous position is present. If so, all telescoping cylinders are retracted synchronously while remaining within certain tolerances. A telescoping cylinder (in principle, any telescoping cylinder) is assigned the task of guiding. This is carried out at the speed corresponding to the deflection of the pre-control transmitter. The telescoping speed of the other cylinders or cylinder stages is adapted in such a way that a synchronous telescoping of all telescoping cylinders occurs while maintaining determined tolerances. If a synchronous position does not exist, the synchronous position is first produced by individual retraction of one or more cylinders. Synchronous retraction then continues in the manner described above.
The same process takes place in an analogous manner for extension. Of course, during subsequent synchronous operation, the guidance task can be assumed by a telescoping cylinder other than that for retraction.